1.)The main difference between the two is that arachnids have eight legs (four pairs of legs) while insects have six (three pairs of legs).
Insects’ bodies are split into three main components: the head (where the eyes, mouth and antennae are found), the thorax (middle section where the legs and sometimes wings are attached) and the abdomen (includes the reproductive organs, gut and sometimes stingers). Arachnids, on the other hand, have only two: the cephalothorax (the head and thorax fused together) and the abdomen.
2.)Spiders:
Because of their broad appetite, many spiders play an important role in their communities by regulating the density of other invertebrate herbivores and predators. ... Spiders that prey on mosquitoes directly lower the numbers of these pests, and can help reduce the spread of mosquito-borne disease.
Insects:
Insects are crucial components of many ecosystems, where they perform many important functions. They aerate the soil, pollinate blossoms, and control insect and plant pests. ... As decomposers, insects help create top soil, the nutrient-rich layer of soil that helps plants grow.
